1. Field of the Invention
This invention relates to a ball grid array integrated circuit package (BGA IC Package) and particularly to a low cost integrated circuit package that has good heat dissipating property and small size.
2. Description of the Prior Art
In semiconductor integrated circuit (IC) industry nowadays, how to make IC packages small size with good heat dissipating property at low cost is a goal almost universally pursued.
In order to resolve the problems of traditional IC package which uses lead frame, a TBGA (Tape Ball Grid Array) package has been developed. FIG. 1 illustrates a typical TBGA package 10 which includes an IC chip 11, a TAB Tape (Tape Automated Bonding Tape) 12 which has metallic circuitry layers 121 formed thereon and a plurality of solder balls 13 attached to the bottom surface of the TAB Tape 12. Between the TAB Tape 12 and the solder balls 13, there is a non-conductive solder ball mask 14 for preventing short circuit of the metallic circuitry 121 resulting from large size solder balls 13.
TBGA package has the advantage of thin TAB Tape 12 (vs. traditional BGA package using printed circuit board as substrate). It is desirable for multi-layer circuit design and may be adapted for etching process. The metallic circuitry 121 may form inner leads 122 toward a center opening formed in the TAB Tape 12. The inner leads 122 are than coupled with bonding pads 111 on the IC chip 11 by means of Tape Automated Bonding (TAB). This method may produce complex metallic circuitry 121 and simplifies packaging process and results in lower cost. The bottom surface of the TAB Tape 12 has large area and thus may support large number of solder balls 13 and leads.
However TBGA package has poor heat dissipating property. A layer of underfilling 15 is usually needed to mold over the top of the chip 11 for protecting the chip 11 and the leads 122. The underfilling 15 which is made from polymer resin (e.g., epoxy) not only adds the height of the package but also has poor heat conductivity, and thus results in poor heat dissipation of the chip 11. This problem becomes a drag to the performance of the chip 11.
In order to fix the problem mentioned above, another TBGA packaging scheme has been introduced. FIG. 2 shows such an example. The TBGA package 20, like the one shown in FIG. 1, also has an IC chip 21, a TAB Tape 22 and a plurality of solder balls 23. There are also inner leads 222 engaged with bonding pads 211 by means of TAB at a center opening of the TAB Tape 22. However the active side of the chip 21 is faced down (toward the TAB Tape 22). The underfilling 25 is molded at the opening below the chip 21 and covers the surrounding area of the opening. The other side of the chip 21 thus may be exposed to outside to enhance heat dissipating effect. However due to the TAB Tape 22 is generally thin and soft, it needs to add a support layer 26 made of epoxy on an opposite side to the solder balls 13 to enhance its mechanical strength. The addition of the support layer 26 increases package thickness and fabrication procedures. It also needs additional equipments and production facilities. Total cost thus will increase. As the active side of the chip 21 is still covered by the underfilling 25, heat dissipating effect does not improve very much.
FIG. 3 shows yet another TBGA package example. Like previous examples, this TBGA package 30 also includes an IC chip 31, a TAB Tape 32, a plurality of solder balls 33 and a bottom underfilling 35. The TAB Tape 32 also has inner leads 322 extending toward a center opening and being soldered with bonding pads 311. However it has a large size heat sink 36 covering the top of the chip 31 and the TAB Tape 32 to dissipate heat more effectively. The heat sink 36 also serves to support the chip 31 and the TAB Tape 32. But the addition of the heat sink 36 also increases total package thickness, fabrication process and production facility investment.
All of this indicates that there is still a lot of room for improvement regard producing low cost IC package which has small size and high heat dissipating property.